1. Field of the Invention
The present invention relates to a leak detector apparatus operating according to the countercurrent principle and including a first high vacuum pump whose inlet is connected to an inlet of the leak detector, a second high vacuum pump whose inlet is connected to a test gas detector, e.g., a mass spectrometer, and a roughing pump whose inlet is connected to the outlets of the high vacuum pumps, and to a leak detection method employing the leak detector apparatus.
2. Description of the Related Art
A leak detector of this type is disclosed in Federal Republic of Germany Pat. No. 2,049,117. A vessel or object to be tested is disposed within a test chamber filled with a test gas of helium or a mixture of helium and air. If the test object leaks, test gas flows in the conveying direction through the leak into the interior of the test object, down through the first high vacuum pump and then, because of the relatively low compression capability for light gases, in the opposite direction through the second high vacuum pump to a mass spectrometer's analyzer tube.
Should a leak detector of this type be subjected to a vessel being tested which has a particularly large leak, there exists the danger that a relatively large amount of test gas can enter the leak detector device. This results not only in temporary overloads, but also in long-term contamination of leak detector apparatus elements, such as the mass spectrometer, where complete removal of the helium constituent of the test gas requires relatively long pumping periods. Moreover, the remaining apparatus elements, particularly the roughing pump, are contaminated with helium for a relatively long period of time so that leak measurements made shortly after an overload are fraught with large errors.
If, as is frequently the custom, the test object is preliminarily evacuated through a separate conduit by means of a roughing pump until it can be connected with the high vacuum pump, then there exists the danger, if there is a particularly large leak in the test object, that most or perhaps even all of the helium present in the test chamber leaks into the test object and is pumped out during the preliminary evacuation. When the test object is subsequently connected to the high vacuum pump and, thus, the actual leak detection begins, very little or no test gas can be detected. The result is that the test object is considered to be leaking only slightly or not at all, although in actuality it leaks considerably.